Your super hero characters have good facial expressions with good intensity. The poses work well too, for in-character effect.
Your lighting on the faces is quite good, but the muscles are often flattened do to lighting angles. Some dark costume elements get lost in the black backgrounds, like yellow Wolverine's boots. Also, his pose makes his body look very shortened from leaning towards the camera. A slight side angle would avoid that effect.
The Dutch Tilted shots can be effective, but be mindful of long hair that is hanging straight down. If you get shots with hair moving, then these tilted shots would work better. The girl with red hair and red costume would look better in a tilted shot if she was standing more leaning forward from the waste, with bent knees.
I like the over-all direction you are going with your super hero portraits. You catch great performances!